Gas sensor, gas sensor installation structure, and method for installing gas sensor

ABSTRACT

A gas sensor includes a sensor element having a specific function, and a housing containing the sensor element therein and including a thread section, and a sealing surface which forms a sealing section together with an installation section at a position deeper than the thread section in a direction in which the sensor element is inserted. When the housing is screwed into the installation section, the release torque of the housing at 850° C. (1123 K) is 9 N·m or more, and an estimated value of a gap formed between the sealing surface and the installation section at 850° C. (1123 K) that is calculated according to a specific equation is 31 μm or less.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 10/396,633,filed Mar. 25, 2003, now U.S. Pat. No. 6,796,175 the entirety of whichis incorporated herein by reference.

This application also claims the benefit of Japanese Application No.2002-095842, filed Mar. 29, 2002, the entirety of which is incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to a gas sensor, a gas sensor installationstructure, and a method for installing gas sensor. More particularly,the present invention relates to a gas sensor which is rarely dislodgedfrom an installation section, even if the gas sensor is installed in avehicle or the like and is used under high temperature conditions, a gassensor installation structure equipped with such a gas sensor, and amethod for installing a gas sensor in such a manner.

BACKGROUND OF THE INVENTION

Various types of gas sensors are installed in the exhaust pipe (pipe) ofa vehicle in order to detect a specific gas component (NO_(x), forexample) contained in exhaust gas. These types of gas sensors aregenerally installed in a specific pipe, such as the pipe 6 of thepresent invention shown in FIG. 1.

In the context of the present invention, a gas sensor 10 includes asensor element 1 having a function of detecting NO_(x) or the like, anda housing 5 which contains the sensor element 1 therein and includes athread section 2 outside the housing and a sealing surface 4 which canform a sealing section 3 by coming in contact with a specific area of aninstallation section (boss 7). The boss 7 having a thread groove whichcan be screwed together with the thread section 2 of the housing 5 issecured to the pipe 6 in which the gas sensor 10 is installed. The gassensor 10 is installed in the pipe 6 by screwing the housing 5 into theboss 7. As shown in FIG. 2, the sealing section 3 may be formed in astate in which a gasket 8 is disposed on the sealing surface 4 wheninstalling the gas sensor 10.

As shown in FIG. 3, there may be a case where a rotating member(rotational hexagon 15), which can be rotated concentrically with thecentral axis of the housing 5, is disposed outside the housing 5, andthe gas sensor 10 is installed so that the sealing surface 4 is pressedagainst the boss 7 by screwing the rotating member without rotating thehousing 5. In the case of using the rotational hexagon 15, the sealingsection 3 may also be formed in a state in which the gasket 8 isdisposed on the sealing surface 4 in the same manner as shown in FIG. 2(see FIG. 4).

Conventionally, in the case where the gas sensor is installed in theinstallation section by screwing the housing at an appropriatetightening torque, the installation area of the gas sensor may besubjected to high temperature when the temperature of the pipe isincreased. For example, in the case where the gas sensor is installed inthe exhaust pipe of a vehicle, the installation area of the gas sensoris subjected to a high temperature of 800-900° C. In this case,depending on the combination of the material for the boss and thematerial for the housing or gasket, a gap is easily formed at thesealing section under high temperature conditions due to the differencein coefficient of thermal expansion between the materials.

If a gap is formed at the sealing section, the tightening force of thescrew is gradually decreased as the gap is increased. If the gas sensoris continuously used in a state in which the tightening force of thescrew is decreased, the gas sensor may be dislodged from the pipe. Inparticular, since the possibility of dislodgement of the gas sensor isincreased when used in an installation environment in which vibration isapplied either continuously or intermittently, measures for eliminatingsuch problems have been demanded.

The present invention has been achieved in view of the above-describedproblems in the conventional art. Accordingly, an object of the presentinvention is to provide a gas sensor which rarely allows the tighteningforce of the screw to be decreased even if the gas sensor is used underhigh temperature conditions when installed in a vehicle or the like, andis rarely dislodged from the pipe or the like in which the gas sensor isinstalled even if vibration is applied, a gas sensor installationstructure equipped with the gas sensor, and a method for installing gassensor.

SUMMARY OF THE INVENTION

According to the present invention, a gas sensor is provided, comprisinga sensor element, which functions to detect a specific gas component, ahousing containing the sensor element therein and having a sealingsurface, a thread section which is adapted to be screwed into a specificinstallation section, and a sealing section formed between the sealingsurface of the housing and a sealing surface of the installation sectionat a position deeper than the thread section in a direction in which thesensor element is inserted. When the housing is screwed into theinstallation section, the release torque of the housing at 850° C. (1123K) is 9 N·m or more, and an estimated value X₁ of a gap formed betweenthe sealing surface of the housing and the sealing surface of theinstallation section at 850° C. (1123 K), that is calculated accordingto the following equation (1), is 31 μm or less:X ₁(μm)={(L ₁×α₁)−(L ₂×α₂)}×1123  (1);wherein X₁ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₂ represents a length (μm) fromthe sealing surface of the housing to a top end of the thread section,α₁ represents a coefficient of thermal expansion (×10⁻⁶/° C.) of theinstallation section, and α₂ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of the housing.

In the present invention, it is preferable that a gasket is provided incontact with the sealing surface of the housing and that an estimatedvalue X₂ of the gap, that is calculated according to equation (2), is 31μm or less:X ₂(μm)={(L ₁×α₁)−(L ₂×α₂)−(L ₃×α₃)}×1123  (2);wherein X₂ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₂ represents a length (μm) fromthe sealing surface of the housing to a top end of the thread section,L₃ represents a thickness (μm) of the gasket, _(α1) represents acoefficient of thermal expansion (×10⁻⁶/° C.) of the installationsection, α₂ represents a coefficient of thermal expansion (×10⁻⁶/° C.)of the housing, and α₃ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of the gasket.

In the present invention, the material for the gasket is preferably atleast one material selected from the group consisting of 430 SS, 304 SS,310 SS, 316 SS, and 321 SS.

According to another aspect of the present invention, a gas sensor isprovided, comprising a sensor element, which functions to detect aspecific gas component, a housing containing the sensor element thereinand having a sealing surface that forms a sealing section together witha sealing surface of an installation section at the front in thedirection in which the sensor element is inserted, and a rotating memberhaving a thread section formed on an outer surface thereof that isadapted to be screwed into the installation section and that can berotated concentrically with respect to a central axis of the housing.When the gas sensor is installed in the installation section by screwingthe rotating member into the installation section, the release torque ofthe rotating member at 850° C. (1123 K) is 9 N·m or more, and anestimated value X₃ of a gap formed between the sealing surface of thehousing and the sealing surface of the installation section at 850° C.(1123 K), that is calculated according to the following equation (3), is31 μm or less:X ₃(μm)={(L ₁×α₁)−(L ₄×α₄)−(L ₅×α₅)}×1123  (3);wherein X₃ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₄ represents a length (μm) from abottom end to a top end of the thread section, L₅ represents a length(μm) from the sealing surface of the housing to the bottom end of thethread section, α₁ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of the installation section, α₄ represents a coefficient ofthermal expansion (×10⁻⁶/° C.) of the rotating member, and α₅ representsa coefficient of thermal expansion (×10⁻⁶/° C.) of the housing.

In the present invention, it is preferable that a gasket is provided incontact with the sealing surface of the housing and that an estimatedvalue X₄ of the gap, that is calculated according to equation (4), is 31μm or less:X ₄(μm)={(L ₁×α₁)−(L ₃×α₃)−(L ₄×α₄)−(L ₅×α₅)}×1123  (4);wherein X₄ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₃ represents a thickness (μm) ofthe gasket, L₄ represents a length (μm) from a bottom end to a top endof the thread section, L₅ represents a length (μm) from the sealingsurface of the housing to the bottom end of the thread section, α₁,represents a coefficient of thermal expansion (×10⁻⁶/° C.) of theinstallation section, α₃ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of the gasket, α₄ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of the rotating member, and α₅ represents acoefficient of thermal expansion (×10⁻⁶/° C.) of the housing.

In the present invention, the material for the gasket is preferably atleast one material selected from the group consisting of 430 SS, 304 SS,310 SS, 316 SS, and 321 SS. In the present invention, the material forthe rotating member is preferably at least one material selected fromthe group consisting of 430 SS, 304 SS, 310 SS, 316 SS, and 321 SS. Thematerial for the housing is preferably at least one material selectedfrom the group consisting of 430 SS, 304 SS, 310 SS, 316 SS, and 321 SS.

According to another aspect of the present invention, a gas sensorinstallation structure is provided, including an installation sectionhaving a sealing surface and a gas sensor. The gas sensor comprises asensor element, which functions to detect a specific gas component, ahousing containing the sensor element therein and having a sealingsurface, a thread section which is adapted to be screwed into theinstallation section, and a sealing section formed between the sealingsurface of the housing and a sealing surface of the installation sectionat a position deeper than the thread section in a direction in which thesensor element is inserted. The gas sensor is installed by screwing thehousing into the installation section. The release torque of the housingat 850° C. (1123 K) is 9 N·m or more, and an estimated value X₅ of a gapformed between the sealing surface of the housing and the sealingsurface of the installation section at 850° C. (1123 K), that iscalculated according to the following equation (5), is 31 μm or less:X ₅(μm)={(L ₁×α₁)−(L ₂×α₂)}×1123  (5);wherein X₂ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₂ represents a length (μm) fromthe sealing surface of the housing to a top end of the thread section,α₁ represents a coefficient of thermal expansion (×10⁻⁶/° C.) of theinstallation section, and α₂ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of the housing.

In the present invention, it is preferable that the sealing section isformed through a gasket and that the estimated value X₆ of the gap, thatis preferably calculated according to equation (6), is 31 μm or less:X ₆(μm)={(L ₁×α₁)−(L ₂×α₂)−(L ₃×α₃)}×1123  (6);wherein X₆ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₂ represents a length (μm) fromthe sealing surface of the housing to a top end of the thread section,L₃ represents a thickness (μm) of the gasket, α₁ represents acoefficient of thermal expansion (×10⁻⁶/° C.) of the installationsection, α₂ represents a coefficient of thermal expansion (×10⁻⁶/° C.)of the housing, and α₃ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of the gasket.

In the present invention, the material for the gasket is preferably atleast one material selected from the group consisting of 430 SS, 304 SS,310 SS, 316 SS, and 321 SS.

According to another aspect of the present invention, a gas sensorinstallation structure is provided, including an installation sectionhaving a sealing surface and a gas sensor. The gas sensor comprises asensor element, which functions to detect a specific gas component, ahousing containing the sensor element therein and having a sealingsurface which forms a sealing section together with the sealing surfaceof the installation section at the front in the direction in which thesensor element is inserted, and a rotating member having a threadsection formed on an outer surface thereof that is adapted to be screwedinto the installation section and that can be rotated concentricallywith respect to a central axis of the housing. The gas sensor isinstalled in the installation section by screwing the rotating memberinto the installation section. The release torque of the rotating memberat 850° C. (1123 K) is 9 N·m or more, and an estimated value X₇ of a gapformed between the sealing surface of the housing and the sealingsurface of the installation section at 850° C. (1123 K), that iscalculated according to the following equation (7), is 31 μm or less:X ₇(μm)={(L ₁×α₁)−(L ₄×α₄)−(L ₅×α₅) }×1123  (7);wherein X₇ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₄ represents a length (μm) from abottom end to a top end of the thread section, L₅ represents a length(μm) from the sealing surface of the housing to the bottom end of thethread section, α₁ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of the installation section, α₄ represents a coefficient ofthermal expansion (×10⁻⁶/° C.) of the rotating member, and α₅ representsa coefficient of thermal expansion (×10⁻⁶/° C.) of the housing.

In the present invention, it is preferable that the sealing section isformed through a gasket and an estimated value X₈ of the gap, that iscalculated according to the following equation (8), is 31 μm or less:X ₈(μm)={(L ₁×α₁)−(L ₃×α₃)−(L ₄×α₄)−(L ₅×α₅)}×1123  (8);wherein X₈ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₃ represents a thickness (μm) ofthe gasket, L₄ represents a length (μm) from a bottom end to a top endof the thread section, L₅ represents a length (μm) from the sealingsurface of the housing to the bottom end of the thread section, α₁represents a coefficient of thermal expansion (×10⁻⁶/° C.) of theinstallation section, α₃ represents a coefficient of thermal expansion(x 10⁻⁶/° C.) of the gasket, α₄ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of the rotating member, and α₅ represents acoefficient of thermal expansion (×10⁻⁶/° C.) of the housing.

In the present invention, the material for the gasket is preferably atleast one material selected from the group consisting of 430 SS, 304 SS,310 SS, 316 SS, and 321 SS. In the present invention, the material forthe rotating member is preferably at least one material selected fromthe group consisting of 430 SS, 304 SS, 310 SS, 316 SS, and 321 SS. Thematerial for the housing is preferably at least one material selectedfrom the group consisting of 430 SS, 304 SS, 310 SS, 316 SS, and 321 SS.

According to another aspect of the present invention, a method forinstalling a gas sensor is provided comprising the steps of providing aninstallation section having a sealing surface and providing a gas sensorwhich comprises a sensor element, which functions to detect a specificgas component, a housing containing the sensor element therein andhaving a sealing surface, a thread section which is adapted to bescrewed into the installation section, and a sealing section formedbetween the sealing surface of the housing and the sealing surface ofthe installation section at a position deeper than the thread section ina direction in which the sensor element is inserted. The gas sensor isinstalled in the installation section by screwing the housing so thatrelease torque of the housing at 850° C. (1123 K) is 9 N·m or more andan estimated value X₉ of a gap formed between the sealing surface of thehousing and the sealing surface of the installation section at 850° C.(1123 K), that is calculated according to the following equation (9), is31 μm or less:X ₉(μm)={(L ₁×α₁)−(L ₂×α₂)}×1123  (9);wherein X₉ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₂ represents a length (μm) fromthe sealing surface of the housing to a top end of the thread section,α₁ represents a coefficient of thermal expansion (×10⁻⁶/° C.) of theinstallation section, and α₂ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of the housing.

In the present invention, it is preferable that the sealing section isformed through a gasket and the housing is screwed so that an estimatedvalue X₁₀ of the gap, that is calculated according to the followingequation (10), is 31 μm or less:X ₁₀(μm)={(L ₁×α₁)−(L ₂×α₂)−(L ₃×α₃)}×1123  (10);wherein X₁₀ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₂ represents a length (μm) fromthe sealing surface of the housing to a top end of the thread section,L₃ represents a thickness (μm) of the gasket, α₁, represents acoefficient of thermal expansion (×10⁻⁶/° C.) of the installationsection, α₂ represents a coefficient of thermal expansion (×10⁻⁶/° C.)of the housing, and α₃ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of the gasket.

According to another aspect of the present invention, a method forinstalling a gas sensor is provided, comprising the steps of providingan installation section having a sealing surface and providing a gassensor, which comprises a sensor element which functions to detect aspecific gas component, a housing containing the sensor element thereinand having a sealing surface which forms a sealing section together withthe sealing surface of the installation section at the front in adirection in which the sensor element is inserted, and a rotating memberhaving a thread section formed on an outer surface thereof that isadapted to be screwed into the installation section and can be rotatedconcentrically with respect to a central axis of the housing. The gassensor is installed in the installation section by screwing the rotatingmember so that release torque of the rotating member at 850° C. (1123 K)is 9 N·m or more and an estimated value X₁₁ of a gap formed between thesealing surface of the housing and the sealing surface of theinstallation section at 850° C. (1123 K), that is calculated accordingto the following equation (11), is 31 μm or less:X ₁₁(μm)={(L ₁×α₁)−(L ₄×α₄)−(L ₅×α₅)}×1123  (11);wherein X₁₁ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₄ represents a length (μm) from abottom end to a top end of the thread section, L₅ represents a length(μm) from the sealing surface of the housing to the bottom end of thethread section, α₁ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of the installation section, α₄ represents a coefficient ofthermal expansion (×10⁻⁶/° C.) of the rotating member, and α₅ representsa coefficient of thermal expansion (×10⁻⁶/° C.) of the housing.

In the present invention, it is preferable that the sealing section isformed through a gasket and that the rotating member is screwed so thatan estimated value X₁₂ of the gap, that is calculated according to thefollowing equation (12), is 31 μm or less:X ₁₂(μm)={(L ₁×α₁)−(L ₃×α₃)−(L ₄×α₄)−(L ₅×α₅)}×1123  (12)wherein X₁₂ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₃ represents a thickness (μm) ofthe gasket, L₄ represents a length (μm) from a bottom end to a top endof the thread section, L₅ represents a length (μm) from the sealingsurface of the housing to the bottom end of the thread section, α₁represents a coefficient of thermal expansion (×10⁻⁶/° C.) of theinstallation section, α₃ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of the gasket, α₄ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of the rotating member, and α₅ represents acoefficient of thermal expansion (×10⁻⁶/° C.) of the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view showing an embodiment of a gassensor installation structure of the present invention.

FIG. 2 is a partial cross-sectional view showing another embodiment ofthe gas sensor installation structure of the present invention.

FIG. 3 is a partial cross-sectional view showing still anotherembodiment of the gas sensor installation structure of the presentinvention.

FIG. 4 is a partial cross-sectional view showing yet another embodimentof the gas sensor installation structure of the present invention.

FIG. 5 is a graph showing the relation between dislodgement of a gassensor and release torque (N·m) and an estimated value (μm) of a gap.

FIG. 6 is a graph in which release torque (N·m) at 850° C. is plottedwith respect to an estimated value of a gap for each gas sensorinstallation structure obtained in examples.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention are described below. However, thepresent invention is not limited to these embodiments. Variousmodifications, improvements, and the like are possible within the scopeof the present invention based on the knowledge of a person skilled inthe art.

According to the present invention, a gas sensor is provided, comprisinga sensor element, which functions to detect a specific gas component, ahousing containing the sensor element therein and having a sealingsurface and a thread section which is adapted to be screwed into aspecific installation section. The sensor element also includes asealing section formed between the sealing surface of the housing and asealing surface of the installation section at a position deeper thanthe thread section in a direction in which the sensor element isinserted. When the housing is screwed into the installation section, therelease torque of the housing at 850° C. (1123 K) is 9 N·m or more, andan estimated value X₁ of a gap formed between the sealing surface of thehousing and the sealing surface of the installation section at 850° C.(1123 K), that is calculated according to the following equation (1), is31 μm or less:X ₁(μm)={(L ₁×α₁)−(L ₂×α₂)}×1123  (1);wherein X₁ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₂ represents a length (μm) fromthe sealing surface of the housing to a top end of the thread section,α₁ represents a coefficient of thermal expansion (×10⁻⁶/° C.) of theinstallation section, and α₂ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of the housing.

The gas sensor of the present invention is described below in detailtaking the gas sensor installation structure shown in FIG. 1 as anexample. FIG. 1 illustrates a state in which the gas sensor 10 isinstalled in the pipe 6 by screwing the housing 5 into the boss 7 asdescribed above. In the case where the relationship between thecoefficient of thermal expansion (α₁) of the boss 7, which is theinstallation section, and the coefficient of thermal expansion (α₂) ofthe housing 5 is α₁>α₂, a gap is formed between the sealing surface 4 ofthe housing 5 and the installation section (boss 7) at the sealingsection 3 when the temperature of the pipe 6 is increased, whereby thetightening force of the screw is decreased. However, in the gas sensorof the present embodiment, since the release torque at 850° C. (1123 K)when the housing 5 is screwed into the installation section (boss 7) andthe estimated value X₁ of the gap calculated according to the aboveequation (1) are specific values in the relationship between thecoefficient of thermal expansion (α₁) of the installation section andthe length (L₁) between the sealing surface of the installation sectionand the top end of the installation section, the tightening force of thethread section 2 is maintained moderately. Therefore, the gas sensor ofthe present embodiment is rarely dislodged from the installation section(boss 7), even if the gas sensor is used in an installation environmentin which vibration is applied either continuously or intermittentlyunder high temperature conditions.

The term “release torque” used in the present invention means the torquenecessary for dislodging the tightened product (gas sensor) from theinstallation section, or the torque necessary to cause the tighteningforce between the tightened product and the installation section to belost, and is a measured value which is actually measured using a torquegauge.

In order to further reduce the possibility of dislodgement, it ispreferable that the release torque at 850° C. (1123 K) when the housingis screwed into the installation section is 15 N·m or more, and that theestimated value X₁ of the gap calculated according to the above equation(1) is 20 μm or less. It is still more preferable that the releasetorque at 850° C. (1123 K) is 20 N·m or more and that the estimatedvalue X₁ of the gap that is calculated according to the above equation(1) is 15 μm or less.

The upper limit of the release torque is not limited in the presentinvention. It is sufficient that the release torque is equal to or lessthan the torque during tightening from the viewpoint of preventingdeformation of the thread section, seizing of the screw, and the like.The lower limit of the estimated value X₁ of the gap in the presentinvention is not limited. There may be a case where the estimated valueX₁ of the gap is a negative value, since the estimated value X₁ is atheoretical value, and it is sufficient that the estimated value X₁ isabout −10 μm or more.

The gas sensor of the present invention may have a configuration inwhich the gasket 8 is provided in contact with the sealing surface 4, asshown in FIG. 2. In this case, an estimated value X₂ of the gap can becalculated according to the following equation (2):X ₂(μm)={(L ₁×α₁)−(L ₂×α₂)−(L ₃×α₃)}×1123  (2);wherein X₂ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₂ represents a length (μm) fromthe sealing surface of the housing to a top end of the thread section,L₃ represents a thickness (μm) of the gasket, α₁ represents acoefficient of thermal expansion (×10⁻⁶/° C.) of the installationsection, α₂ represents a coefficient of thermal expansion (×10⁻⁶/° C.)of the housing, and α₃ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of the gasket.

According to another aspect of the present invention, a gas sensor isprovided, comprising a sensor element, which functions to detect aspecific gas component, a housing containing the sensor element thereinand having a sealing surface which forms a sealing section together witha sealing surface of an installation section at the front in a directionin which the sensor element is inserted, and a rotating member having athread section formed on an outer surface thereof that is adapted to bescrewed into the installation section and that can be rotatedconcentrically with respect to a central axis of the housing. When thegas sensor is installed in the installation section by screwing therotating member into the installation section, the release torque of therotating member at 850° C. (1123 K) is 9 N·m or more, and an estimatedvalue X₃ of a gap formed between the sealing surface of the housing andthe sealing surface of the installation section at 850° C. (1123 K),that is calculated according to the following equation (3), is 31 μm orless:X ₃(μm)={(L ₁×α₁)−(L ₄×α₄)−(L ₅×α₅)}×1123  (3);wherein X₃ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₄ represents a length (μm) from abottom end to a top end of the thread section, L₅ represents a lengthfrom the sealing surface of the housing to the bottom end of the threadsection (μm), α₁ represents a coefficient of thermal expansion (×10⁻⁶/°C.) of the installation section, α₄ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of the rotating member, and α₅ represents acoefficient of thermal expansion (×10⁻⁶/° C.) of the housing.

The gas sensor of the present invention is described below taking thegas sensor installation structure shown in FIG. 3 as an example.

As described above, FIG. 3 illustrates a state in which the rotatingmember (rotational hexagon 15) which can be rotated concentrically withrespect to the central axis of the housing 5 is disposed outside thehousing 5, and the gas sensor 10 is installed by screwing the rotatingmember so that the sealing surface 4 of the housing 5 is pressed againsta sealing surface of the installation section (boss 7) without rotatingthe housing 5. In the case where the relationship between thecoefficient of thermal expansion (α₁) of the boss 7, which is theinstallation section, and the coefficients of thermal expansion (α₄ andα₅) of the housing 5 and the rotating member (rotational hexagon 15) isα₁>α₄ and α₁>α₅, a gap is formed between the sealing surface 4 of thehousing 5 and the installation section (boss 7) at the sealing section 3when the temperature of the pipe 6 is increased, whereby the tighteningforce of the screw is decreased. However, in the gas sensor of thepresent embodiment, since the value of the release torque at 850° C.(1123 K), when the rotational hexagon 15 (which is the rotating member)is screwed into the installation section (boss 7), and the estimatedvalue X₃ of the gap that is calculated according to the above equation(3), are specific values in the relationship between the coefficient ofthermal expansion (α₁) of the installation section and the length (L₁)between the sealing surface of the installation section and the top endof the installation section, the tightening force of the thread section2 is maintained moderately. Therefore, the gas sensor of the presentembodiment is rarely dislodged from the installation section (boss 7)even if the gas sensor is used in an installation environment in whichvibration is applied either continuously or intermittently under hightemperature conditions.

In order to further reduce the possibility of dislodgement, it ispreferable that the release torque at 850° C. (1123 K), when therotating member is screwed into the installation section, is 15 N·m ormore and that the estimated value X₃ of the gap that is calculatedaccording to the above equation (3) is 20 μm or less. It is still morepreferable that the release torque at 850° C. (1123 K) is 20 N·m or moreand the estimated value X₃ of the gap that is calculated according tothe above equation (3) is 15 μm or less.

In the present invention, the upper limit of the release torque is notlimited. It is sufficient that the release torque is equal to or lessthan the torque during tightening from the viewpoint of preventingdeformation of the thread section, seizing of the screw, and the like.The lower limit of the estimated value X₁ of the gap in the presentinvention is not limited. There may be a case where the estimated valueX₃ of the gap is a negative value since the estimated value X₃ is atheoretical value, and it is sufficient that the estimated value X₃ isabout −10 μm or more.

In the present invention, a configuration in which the gasket 8 isprovided in contact with the sealing surface 4, as shown in FIG. 4, maybe employed. In this case, an estimated value X₄ of the gap can becalculated according to the following equation (4):X ₄(μm)={(L ₁×α₁)−(L ₃×α₃)−(L ₄×α₄)−(L ₅×α₅)}×1123  (4);wherein X₄ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₃ represents a thickness (μm) ofthe gasket, L₄ represents a length (μm) from a bottom end to a top endof the thread section, L₅ represents a length (μm) from the sealingsurface of the housing to the bottom end of the thread section, α₁represents a coefficient of thermal expansion (×10⁻⁶/° C.) of theinstallation section, α₃ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of the gasket, α₄ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of the rotating member, and α₅ represents acoefficient of thermal expansion (×10⁻⁶/° C.) of the housing.

In the present invention, the material for the gasket is preferably atleast one material selected from the group consisting of 430 SS, 304 SS,310 SS, 316 SS, and 321 SS. These materials can exhibit superior sealingproperties at the sealing section and have excellent workability.

In the present invention, general-purpose materials are suitably used asthe materials that make up the rotating member and the housing. Asspecific examples of the material for the rotating member, at least onematerial selected from the group consisting of 430 SS, 304 SS, 310 SS,316 SS, and 321 SS is preferably used. As specific examples of thematerial for the housing, at least one material selected from the groupconsisting of 430 SS, 304 SS, 310 SS, 316 SS, and 321 SS is preferablyused.

According to another aspect of the present invention, a gas sensorinstallation structure is provided, including an installation sectionhaving a sealing surface and a gas sensor. The gas sensor comprises asensor element, which functions to detect a specific gas component, ahousing containing the sensor element therein and having a sealingsurface, a thread section which is adapted to be screwed into theinstallation section, and a sealing section formed between the sealingsurface of the housing and the sealing surface of the installationsection at a position deeper than the thread section in a direction inwhich the sensor element is inserted. The gas sensor is installed byscrewing the housing into the installation section. The release torqueof the housing at 850° C. (1123 K) of the housing is 9 N·m or more, andan estimated value X₅ of a gap formed between the sealing surface of thehousing and the sealing surface of the installation section at 850° C.(1123 K), that is calculated according to the following equation (5), is31 μm or less:

 X ₅(μm)={(L ₁×α₁)−(L ₂×α₂)}×1123  (5);

wherein X₂ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₂ represents a length (μm) fromthe sealing surface of the housing to a top end of the thread section,α₁ represents a coefficient of thermal expansion (×10⁻⁶/° C.) of theinstallation section, and α₂ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of the housing.

The gas sensor installation structure of the present invention isdescribed below taking the gas sensor installation structure shown inFIG. 1 as an example.

As described above, a gap is formed between the sealing surface 4 of thehousing 5 and the installation section 7 at the sealing section 3 whenthe temperature of the pipe 6 is increased, whereby the tightening forceof the screw is decreased. However, in the gas sensor installationstructure of the present embodiment, since the release torque at 850° C.(1123 K) and the estimated value X₅ of the gap calculated according tothe above equation (5) are specific values, the tightening force of thethread section 3 is maintained moderately. Therefore, even if the gassensor installation structure of the present embodiment is used in aninstallation environment in which vibration is applied eithercontinuously or intermittently under high temperature conditions, thegas sensor 10 is significantly rarely dislodged from the installationsection (boss 7).

In order to further reduce the possibility of dislodgement, it ispreferable that the release torque of the housing at 850° C. (1123 K) is15 N·m or more and that the estimated value X₅ of the gap that iscalculated according to the above equation (5) is 20 μm or less. It isstill more preferable that the release torque at 850° C. (1123 K) is 20N·m or more and that the estimated value X₅ of the gap that iscalculated according to the above equation (5) is 15 μm or less.

In the present invention, the upper limit of the release torque is notlimited. It is sufficient that the release torque is equal to or lessthan the torque during tightening from the viewpoint of preventingdeformation of the thread section, seizing of the screw, and the like.The lower limit of the estimated value X₁ of the gap in the presentinvention is not limited. There may be a case where the estimated valueX₅ of the gap is a negative value since the estimated value X₅ is atheoretical value, and it is sufficient that the estimated value X₅ isabout −10 μm or more.

The gas sensor installation structure of the present invention may havea configuration in which the sealing section 3 is formed through thegasket 8, as shown in FIG. 2. In this case, an estimated value X₆ of thegap can be calculated according to the following equation (6):

 X ₆(μm)={(L ₁×α₁)−(L ₂×α₂)−(L ₃×α₃)}×1123  (6);

wherein X₆ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₂ represents a length (μm) fromthe sealing surface of the housing to a top end of the thread section,L₃ represents a thickness (μm) of the gasket, α₁ represents acoefficient of thermal expansion (×10⁻⁶/° C.) of the installationsection, α₂ represents a coefficient of thermal expansion (×10⁻⁶/° C.)of the housing, and α₃ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of the gasket.

In the present invention, the material for the gasket is preferably atleast one material selected from the group consisting of 430 SS, 304 SS,310 SS, 316 SS, and 321 SS. These materials can exhibit superior sealingproperties at the sealing section and have excellent workability.

According to another aspect of the present invention, a gas sensorinstallation structure is provided, including an installation sectionhaving a sealing surface and a gas sensor. The gas sensor comprises asensor element, which functions to detect a specific gas component, ahousing containing the sensor element therein and having a sealingsurface which forms a sealing section together with the sealing surfaceof the installation section at the front in a direction in which thesensor element is inserted, and a rotating member having a threadsection formed on an outer surface thereof that is adapted to be screwedinto the installation section and that can be rotated concentricallywith respect to a central axis of the housing. The gas sensor isinstalled in the installation section by screwing the rotating memberinto the installation section. The release torque of the rotating memberat 850° C. (1123 K) is 9 N·m or more, and an estimated value X₇ of a gapformed between the sealing surface of the housing and the sealingsurface of the installation section at 850° C. (1123 K), that iscalculated according to the following equation (7), is 31 μm or less:X ₇(μm)={(L ₁×α₁)−(L ₄×α₄)−(L ₅×α₅)}×1123  (7);wherein X₇ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₄ represents a length (μm) from abottom end to a top end of the thread section, L₅ represents a length(μm) from the sealing surface of the housing to the bottom end of thethread section, α₁ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of the installation section, α₄ represents a coefficient ofthermal expansion (×10⁻⁶/° C.) of the rotating member, and α₅ representsa coefficient of thermal expansion (×10⁻⁶/° C.) of the housing.

The gas sensor installation structure of the present invention isdescribed below taking the gas sensor installation structure shown inFIG. 3 as an example.

FIG. 3 illustrates a state in which the rotating member (rotationalhexagon 15), which can be rotated concentrically with the center axis ofthe housing 5, is disposed outside the housing 5, and the gas sensorinstallation structure is formed by screwing the rotating member so thatthe sealing surface 4 is pressed against the boss 7 without rotating thehousing 5. In the case where the relationship between the coefficient ofthermal expansion (α₁) of the boss 7, which is the installation section,and the coefficients of thermal expansion (α₄ and α₅) of the housing 5and the rotating member (rotational hexagon 15) is α₁>α₄ and α₁>α₅, agap is formed between the sealing surface 4 of the housing 5 and theinstallation section 7 at the sealing section 3 when the temperature ofthe pipe 6 is increased, whereby the tightening force of the screw isdecreased. However, in the gas sensor installation structure of thepresent invention, since the release torque at 850° C. (1123 K) and theestimated value X₇ of the gap calculated according to the above equation(7) are specific values, the tightening force of the thread section 2 ismaintained moderately. Therefore, even if the gas sensor installationstructure of the present embodiment is used in an installationenvironment in which vibration is applied either continuously orintermittently under high temperature conditions, the gas sensor issignificantly rarely dislodged from the installation section (boss 7).

In order to further reduce the possibility of dislodgement, it ispreferable that the release torque of the rotating member at 850° C.(1123 K) is 15 N·m or more and the estimated value X₇ of the gap that iscalculated according to the above equation (7) is 20 μm or less. It isstill more preferable that the release torque of the rotating member at850° C. (1123 K) is 20 N·m or more and the estimated value X₇ of the gapcalculated according to the above equation (7) is 15 μm or less.

In the present invention, the upper limit of the release torque of therotating member is not limited. It is sufficient that the release torqueis equal to or less than the torque during tightening from the viewpointof preventing deformation of the thread section, seizing of the screw,and the like. The lower limit of the estimated value X₁ of the gap inthe present invention is not limited. There may be a case where theestimated value X₇ of the gap is a negative value since the estimatedvalue X₇ is a theoretical value, and it is sufficient that the estimatedvalue X₇ is about −10 μm or more.

The gas sensor installation structure of the present invention may havea configuration in which the sealing section 3 is formed through thegasket 8, as shown in FIG. 4. In this case, an estimated value X₈ of thegap can be calculated according to the following equation (8):

 X ₈(μm)={(L ₁×α₁)−(L ₃×α₃)−(L ₄×α₄)−(L ₅×α₅)}×1123  (8)

wherein X₈ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₃ represents a thickness (μm) ofthe gasket, L₄ represents a length (μm) from a bottom end to a top endof the thread section, L₅ represents a length (μm) from the sealingsurface of the housing to the bottom end of the thread section, α₁represents a coefficient of thermal expansion (×10⁻⁶/° C.) of theinstallation section, α₃ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of the gasket, α₄ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of the rotating member, and α₅ represents acoefficient of thermal expansion (×10⁻⁶/° C.) of the housing.

In this case, the material for the gasket is preferably at least onematerial selected from the group consisting of 430 SS, 304 SS, 310 SS,316 SS, and 321 SS. These materials can exhibit superior sealingproperties at the sealing section and have excellent workability.

In the present invention, general-purpose materials are suitably used asthe materials for the rotating member and the housing. As the materialfor the rotating member, at least one material selected from the groupconsisting of 430 SS, 304 SS, 310 SS, 316 SS, and 321 SS is preferablyused. As the material for the housing, at least one material selectedfrom the group consisting of 430 SS, 304 SS, 310 SS, 316 SS, and 321 SSis preferably used.

A method for installing gas sensor of the present invention is describedbelow. According to the present invention, a method for installing a gassensor is provided, comprising the steps of providing an installationsection having a sealing surface and providing a gas sensor. The gassensor comprises a sensor element, which functions to detect a specificgas component, a housing containing the sensor element therein andhaving a sealing surface, a thread section which is adapted to bescrewed into the installation section, and a sealing section formedbetween the sealing surface of the housing and the sealing surface ofthe installation section at a position deeper than the thread section ina direction in which the sensor element is inserted. The gas sensor isinstalled in the installation section by screwing the housing so thatrelease torque of the housing at 850° C. (1123 K) is 9 N·m or more andan estimated value X₉ of a gap formed between the sealing surface of thehousing and the sealing surface of the installation section at 850° C.(1123 K), that is calculated according to the following equation (9), is31 μm or less:X ₉(μm)={(L ₁×α₁)−(L ₂×α₂)}×1123  (9);wherein X₉ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₂ represents a length (μm) fromthe sealing surface of the housing to a top end of the thread section,α₁ (represents a coefficient of thermal expansion (×10⁻⁶/° C.) of theinstallation section, and α₂ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of the housing.

The method for installing gas sensor is described below taking the gassensor installation structure shown in FIG. 1 as an example.

In the case where the relationship between the coefficient of thermalexpansion (α₁) of the boss 7, which is the installation section, and thecoefficient of thermal expansion (α₂) of the housing 5 is α₁>α₂, a gapis formed between the sealing surface 4 of the housing 5 and theinstallation section 7 at the sealing section 3 when the temperature ofthe pipe 6 is increased, whereby the tightening force of the screw isdecreased. However, in the method for installing gas sensor of thepresent invention, since the housing is screwed so that the releasetorque at 850° C. (1123 K) and the estimated value X₉ of the gap formedbetween the sealing surface 4 and the installation section (boss 7) at850° C. (1123 K), that is calculated according to the above equation(9), are specific values, a gas sensor installation structure in which amoderate contact pressure is maintained in the sealing section 3 even ata high temperature of 800-900° C. can be obtained, for example.Therefore, a gas sensor installation structure in which the gas sensor10 is significantly rarely dislodged from the installation section (boss7), even if the gas sensor installation structure is used in aninstallation environment in which vibration is applied eithercontinuously or intermittently under high temperatures conditions, canbe provided.

In order to further reduce the possibility of dislodgement, it ispreferable to screw the housing so that the release torque at 850° C.(1123 K) is 15 N·m or more and the estimated value X₉ of the gap, thatis calculated according to the above equation (9), is 20 μm or less. Itis still more preferable to screw the housing so that the release torqueat 850° C. (1123 K) is 20 N·m or more and the estimated value X₉ of thegap calculated according to the above equation (9) is 15 μm or less.

In the present invention, the upper limit of the release torque is notlimited. It is sufficient that the release torque is equal to or lessthan the torque during tightening from the viewpoint of preventingdeformation of the thread section, seizing of the screw, and the like.The lower limit of the estimated value X₁ of the gap in the presentinvention is not limited. There may be a case where the estimated valueX₉ of the gap is a negative value since the estimated value X₉ is atheoretical value, and it is sufficient that the estimated value X₉ isabout −10 μm or more.

In the method for installing gas sensor of the present invention, thesealing section 3 may be formed through the gasket 8, as shown in FIG.2. In this case, an estimated value X₁₀ of the gap can be calculatedaccording to the following equation (10):X ₁₀(μm)={(L ₁×α₁)−(L ₂×α₂)−(L ₃×α₃)}×1123  (10);wherein X₁₀ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₂ represents a length (μm) fromthe sealing surface of the housing to a top end of the thread section,L₃ represents a thickness (μm) of the gasket, α₁ represents acoefficient of thermal expansion (×10⁻⁶/° C.) of the installationsection, α₂ represents a coefficient of thermal expansion (×10⁻⁶/° C.)of the housing, and α₃ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of the gasket.

According to another aspect of the present invention, a method forinstalling a gas sensor is provided, comprising the steps of providingan installation section having a sealing surface and providing a gassensor. The gas sensor comprises a sensor element, which functions todetect a specific gas component, a housing containing the sensor elementtherein and having a sealing surface which forms a sealing sectiontogether with the sealing surface of the installation section at thefront in a direction in which the sensor element is inserted, and arotating member having a thread section formed on an outer surfacethereof that is adapted to be screwed into the installation section andthat can be rotated concentrically with respect to a central axis of thehousing. The gas sensor is installed in the installation section byscrewing the rotating member so that a release torque of the rotatingmember at 850° C. (1123 K) is 9 N·m or more and an estimated value X₁₁of a gap formed between the sealing surface of the housing and thesealing surface of the installation section at 850° C. (1123 K), that iscalculated according to the following equation (11), is 31 μm or less:X ₁₁(μm)={(L ₁×α₁)−(L ₄×α₄)−(L ₅×α₅)}×1123  (11);wherein X₁₁ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₄ represents a length (μm) from abottom end to a top end of the thread section, L₅ represents a length(μm) from the sealing surface of the housing to the bottom end of thethread section, α₁ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of the installation section, α₄ represents a coefficient ofthermal expansion (×10⁻⁶/° C.) of the rotating member, and α₅ representsa coefficient of thermal expansion (×10⁻⁶/° C.) of the housing.

The method for installing gas sensor is described below taking the gassensor installation structure shown in FIG. 3 as an example.

FIG. 3 illustrates a state in which the rotating member (rotationalhexagon 15), which can be rotated concentrically with respect to thecentral axis of the housing 5, is disposed outside the housing 5, andthe gas sensor installation structure is formed by screwing the rotatingmember so that the sealing surface 4 is pressed against the boss 7without rotating the housing 5. In the case where the relationshipbetween the coefficient of thermal expansion (α₁) of the boss 7 which isthe installation section and the coefficients of thermal expansion (α₄and α₅) of the housing 5 and the rotating member (rotational hexagon 15)is α₁>α₄ and α₁>α₅, a gap is formed between the sealing surface 4 of thehousing 5 and the installation section (boss 7) at the sealing section 3when the temperature of the pipe 6 is increased in this state, wherebythe tightening force of the thread section 3 is decreased.

However, in the method for installing gas sensor of the presentinvention, since the rotational hexagon 15 is screwed so that therelease torque at 850° C. (1123 K) and the estimated value X₁₁ of thegap formed between the sealing surface 4 and the installation section(boss 7) at 850° C. (1123 K), that is calculated according to the aboveequation (11), are specific values, a gas sensor installation structurein which a moderate contact pressure is maintained in the sealingsection 3 even at a high temperature of 800-900° C. can be obtained.Therefore, a gas sensor installation structure in which the gas sensor10 is significantly rarely dislodged from the installation section (boss7) even if the gas sensor installation structure is used in aninstallation environment in which vibration is applied eithercontinuously or intermittently under high temperature conditions can beprovided.

In order to further reduce the possibility of dislodgement, it ispreferable to screw the rotating member so that the release torque at850° C. (1123 K) is 15 N·m or more and the estimated value X₁₁ of thegap calculated according to the above equation (11) is 20 μm or less. Itis still more preferable to screw the rotating member so that therelease torque at 850° C. (1123 K) is 20 N·m or more and the estimatedvalue X₁₁ of the gap calculated according to the above equation (11) is15 μm or less.

In the present invention, the upper limit of the release torque is notlimited. It is sufficient that the release torque is equal to or lessthan the torque during tightening from the viewpoint of preventingdeformation of the thread section, seizing of the screw, and the like.The lower limit of the estimated value X₁₁ of the gap in the presentinvention is not limited. There may be a case where the estimated valueX₁₁ of the gap is a negative value since the estimated value X₁₁ is atheoretical value. It is sufficient that the estimated value X₁₁ isabout −10 μm or more.

In the method for installing gas sensor of the present invention, thesealing section 3 may be formed through the gasket 8, as shown in FIG.4. In this case, an estimated value X₁₂ of the gap can be calculatedaccording to the following equation (12):X ₁₂(μm)={(L ₁×α₁)−(L ₃×α₃)−(L ₄×α₄)−(L ₅×α₅)}×1123  (12);wherein X₁₂ represents an estimated value (μm) of the gap, L₁ representsa length (μm) from the sealing surface of the installation section to atop end of the installation section, L₃ represents a thickness (μm) ofthe gasket, L₄ represents a length (μm) from a bottom end to a top endof the thread section, L₅ represents a length (μm) from the sealingsurface of the housing to the bottom end of the thread section, α₁represents a coefficient of thermal expansion (×10⁻⁶/° C.) of theinstallation section, α₃ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of the gasket, α₄ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of the rotating member, and α₅ represents acoefficient of thermal expansion (×10⁻⁶/° C.) of the housing.

In the method for installing gas sensor of the present invention,general-purpose materials are suitably used as the materials for thegasket, the rotating member, and the housing. As the material for thegasket, at least one material selected from the group consisting of 430SS, 304 SS, 310 SS, 316 SS, and 321 SS is preferably used. As thematerial for the rotating member, at least one material selected fromthe group consisting of 430 SS, 304 SS, 310 SS, 316 SS, and 321 SS ispreferably used. As the material for the housing, at least one materialselected from the group consisting of 430 SS, 304 SS, 310 SS, 316 SS,and 321 SS is preferably used.

EXAMPLES

The present invention is described below in more detail by examples.However, the present invention is not limited by these examples.

Relationship Between Dislodgement of Gas Sensor, Release Torque andEstimated Value of Gap:

Each constituent member formed of the materials shown in Table 1 wasprovided. The rotational hexagon was screwed into the boss at atightening torque of 30 N·m or more at room temperature to obtain a gassensor installation structure having a structure shown in FIG. 3(samples Nos. 1-13). The length (L₁: mm) from the sealing surface to thetop end of the boss (installation section) is shown in Table 1. Theresulting gas sensor installation structures were allowed to stand underhigh temperature conditions of 850° C., and the release torque (N·m) ofthe rotational hexagon was measured. The estimated value (μm) of the gapformed between the sealing surface and the boss was calculated from thecoefficient of thermal expansion (×10⁻⁶/° C.) of the materials for eachmember and the lengths (mm) at each point (L₁ and L₃ to L₅). FIG. 5 is agraph in which the release torque (N·m) is plotted with respect to theresulting estimated values. The resulting gas sensor installationstructures were subjected to a vibration test to confirm whether or notthe gas sensor was dislodged. The results are shown in FIG. 5.

TABLE 1 Material Sample Rotational Length No. Boss Housing Gaskethexagon (L1: mm) 1 316 SS 430 SS 430 SS 430 SS 9.5 2 316 SS 430 SS 430SS 304 SS 9.5 3 304 SS 430 SS 430 SS 316 SS 9.5 4 316 SS 430 SS 430 SS430 SS 11 5 304 SS 430 SS 430 SS 304 SS 9.5 6 316 SS 430 SS 430 SS 304SS 9.5 7 316 SS 430 SS — 304 SS 9.5 8 316 SS 430 SS — 304 SS 9.5 9 316SS 430 SS — 304 SS 9.5 10 304 SS 430 SS 430 SS 304 SS 9.5 11 304 SS 430SS — 304 SS 9.5 12 304 SS 430 SS — 304 SS 9.5 13 304 SS 430 SS — 304 SS9.5

As is clear from the results shown in FIG. 5, it was the gas sensor isnot dislodged from the boss, which stallation section, when the releasetorque of the hexagon at 850° C. (1123 K) is 9 N·m or more and the valueof the gap is 31 μm or less. Specifically, it was found that the gassensor can be prevented from being dislodged in advance by appropriatelyselecting the materials and dimensions of the rotational hexagon, thegasket, and the housing for the material and dimensions of the boss, andappropriately controlling the tightening force (release torque) of therotational hexagon.

Measurement of Release Torque:

The release torque of the rotational hexagon (rotating member) of thegas sensor installation structure was measured according to thefollowing method. The gas sensor installation structure was formed byinstalling the gas sensor in the pipe. The gas sensor installationstructure was then heated by allowing gas at 850° C. to flow through thepipe. After allowing the gas sensor installation structure to stand fortwo hours in this state, the release torque measured using a torquegauge was taken as the release torque (N·m) at 850° C.

Vibration Test:

The gas sensor installation structure thus obtained was subjected to avibration test using test equipment and conditions shown in Table 2.

TABLE 2 Test equipment Propane burner Gas temperature 850° C. Frequency50-250 Hz Acceleration 30-50 G

Examples 1-4 and Comparative Examples 1-2

Each constituent member formed of the materials shown in Table 3 wasprovided. The rotational hexagon was screwed into the boss at atightening torque of 60 N·m or 40 N·m at room temperature to obtain agas sensor installation structure having a structure shown in FIG. 3.The gas sensor installation structure thus obtained was allowed to standunder high temperature conditions of 850° C., and the release torque(N·m) of the rotational hexagon was measured. The estimated value (μm)of the gap formed between the sealing surface and the boss wascalculated from the coefficients of thermal expansion (×10⁻⁶/° C.) ofthe materials for each member and the lengths (mm) at each point (L₁ andL₃ to L₅). Table 3 shows the release torque (N·m) at 850° C. and theestimated value (μm) of the gap. FIG. 6 shows a graph in which therelease torque (N·m) at 850° C. is plotted with respect to the estimatedvalue of the gap.

TABLE 3 Tightening torque Material 60 N · m 40 N · m EstimatedRotational Release torque value of hexagon Housing Boss at 850° C. (N ·m) gap (μm) Dislodgement Example 1 304 SS 430 SS 304 SS 34 30.9 −1.2None Example 2 304 SS 430 SS 316 SS 25.4 19.7 6.4 None Example 3 304 SS430 SS 304 SS 34 30.9 −1.2 None Example 4 304 SS 430 SS 316 SS 25.4 19.76.4 None Comparative 430 SS 430 SS 316 SS 8 0 32.8 Dislodged Example 1Comparative 430 SS 430 SS 316 SS 8 0 32.8 Dislodged Example 2

The gas sensor installation structures thus obtained were subjected tothe vibration test to confirm whether or not the gas sensor wasdislodged. As a result, although the gas sensor was not dislodged inExamples 1-4, the gas sensor was dislodged in Comparative Examples 1 and2 (see Table 3). Therefore, as shown in FIG. 6, it was confirmed thatthe gas sensor is not dislodged from the boss, which is the installationsection, in the case where the release torque of the rotational hexagonat 850° C. (1123 K) is 9 N·m or more and the estimated value of the gapis 31 μm or less.

As described above, the gas sensor of the present invention rarelyallows the tightening force of the screw to be decreased, even if thegas sensor is installed and used under high temperature conditions, andis rarely dislodged from the installation section, even if vibration isapplied, since the release torque at a specific temperature in the casewhere the housing or the rotating member which is the constituent memberis screwed into the installation section and the estimated value of thegap formed between the sealing surface of the housing and theinstallation section are specific values. The gas sensor installationstructure of the present invention rarely allows the tightening force ofthe screw to be decreased even if the gas sensor installation structureis installed and used under high temperature conditions, and the gassensor is rarely dislodged from the installation section even ifvibration is applied, since the release torque of the housing or therotating member at a specific temperature and the estimated value of thegap formed between the sealing surface and the installation section arespecific values.

According to the method for installing gas sensor of the presentinvention, since the housing or the rotating member is screwed so thatthe release torque at a specific temperature and the estimated value ofthe gap formed between the sealing surface and the installation sectionare specific values, a gas sensor installation structure in which thegas sensor is significantly rarely dislodged from the installationsection can be obtained.

1. A gas sensor comprising a sensor element for detecting a specific gascomponent, a housing which contains said sensor element therein and hasa sealing surface which forms a sealing section together with aninstallation section at the front in a direction in which said sensorelement in inserted, and a rotating member which has a thread sectionwhich is formed outside said rotating member and is to be screwed intothe installation section and can be rotated concentrically with respectto a central axis of said housing; wherein when said gas sensor isinstalled in the installation section by screwing said rotating memberinto the installation section, a release torque of said rotating memberat 850° C. (1123 K) is 9 N·m or more; and wherein an estimated value X₃of a gap formed between said sealing surface of said housing and asealing surface of the installation section at 850° C. (1123 K), that iscalculated according to the following equation, is 31 μm or less:X ₃(μm)={(L ₁×α₁)−(L ₄×α₄)−(L ₅×α₅)}×1123; wherein X₃ represents anestimated value (μm) of the gap, L₁ represents a length (μm) from thesealing surface of the installation section to a top end of theinstallation section, L₄ represents a length (μm) from a bottom end to atop end of said thread section, L₅ represents a length (μm) from saidsealing surface of said housing to the bottom end of said threadsection, α₁ represents a coefficient of thermal expansion (×10⁻⁶/° C.)of the installation section, α₄ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of said rotating member, and α₅ represents acoefficient of thermal expansion (×10⁻⁶/° C.) of said housing.
 2. Thegas sensor according to claim 1, wherein a gasket is provided in contactwith said sealing surface of said housing and an estimated value X₄ ofthe gap, that is calculated according to the following equation, is 31μm or less:X ₄(μm)={(L ₁×α₁)−(L ₃ ×α₃)−(L ₄×α₄)−(L ₅×α₅)}×1123; wherein X₄represents an estimated value (μm) of the gap, L₁ represents a length(μm) from the sealing surface of the installation section to a top endof the installation section, L₃ represents a thickness (μm) of saidgasket, L₄ represents a length (μm) from a bottom end to a top end ofsaid thread section, L₅ represents a length (μm) from said sealingsurface of said housing to the bottom end of said thread section, α₁represents a coefficient of thermal expansion (×10⁻⁶/° C.) of theinstallation section, α₃ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of said gasket, α₄ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of said rotating member, and α₅ represents acoefficient of thermal expansion (×10⁻⁶/° C.) of said housing.
 3. Thegas sensor according to claim 2, wherein said gasket comprises at leastone material selected from the group consisting of 430 SS, 304 SS, 310SS, 316 SS, and 321 SS.
 4. The gas sensor according to claim 1, whereinsaid rotating member comprises at least one material selected from thegroup consisting of 430 SS, 304 SS, 310 SS, 316 SS, and 321 SS.
 5. A gassensor installation structure comprising: an installation section; and agas sensor comprising a sensor element for detecting a specific gascomponent, a housing which contains said sensor element therein and hasa sealing surface which forms a sealing section together with saidinstallation section at the front in a direction in which said sensorelement is inserted, and a rotating member which has a thread sectionwhich is formed outside said rotating member and is screwed into saidinstallation section and can be rotated concentrically with respect to acentral axis of said housing; wherein said gas sensor is installed insaid installation section by screwing said rotating member into saidinstallation section; wherein a release torque of said rotating memberat 850° C. (1123 K) is 9 N·m or more; and wherein an estimated value X₇of a gap formed between said sealing surface of said housing and asealing surface of said installation section at 850° C. (1123 K), thatis calculated according to the following equation, is 31 μm or less:X ₇(μm)={(L ₁×α₁)−(L ₄×α₄)−(L ₅×α₅)}×1123; wherein X₇ represents anestimated value (μm) of said gap, L₁ represents a length (μm) from saidsealing surface of said installation section to a top end of saidinstallation section, L₄ represents a length (μm) from a bottom end to atop end of said thread section, L₅ represents a length (μm) from saidsealing surface of said housing to the bottom end of said threadsection, α₁ represents a coefficient of thermal expansion (×10⁻⁶/° C.)of said installation section, α₄ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of said rotating member, and α₅ represents acoefficient of thermal expansion (×10⁻⁶/° C.) of said housing.
 6. Thegas sensor installation structure according to claim 5, wherein saidsealing section is formed through a gasket and an estimated value X₈ ofsaid gap, that is calculated according to the following equation, 31 μmor less:X ₈(μm)={(L ₁×α₁)−(L ₃×α₃)−(L ₄×α₄)−(L ₅×α₅)}×1123; wherein X₈represents an estimated value (μm) of said gap, L₁ represents a length(μm) from said sealing surface of said installation section to a top endof said installation section, L₃ represents a thickness (μm) of saidgasket, L₄ represents a length (μm) from a bottom end to a top end ofsaid thread section, L₅ represents a length (μm) from said sealingsurface of said housing to the bottom end of said thread section, α₁represents a coefficient of thermal expansion (×10⁻⁶/° C.) of saidinstallation section, α₃ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of said gasket, α₄ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of said rotating member, and α₅ represents acoefficient of thermal expansion (×10⁻⁶/° C.) of said housing.
 7. Thegas sensor installation structure according to claim 6, wherein saidgasket comprises at least one material selected from the groupconsisting of 430 SS, 304 SS, 310 SS, 316 SS, and 321 SS.
 8. The gassensor installation structure according to claim 5, wherein saidrotating member comprises at least one material selected from the groupconsisting of 430 SS, 304 SS, 310 SS, 316 SS, and 321 SS.
 9. A methodfor installing a gas sensor comprising the steps of: providing aninstallation section having a sealing surface; providing a gas sensorcomprising a sensor element for detecting a specific gas component, ahousing which contains said sensor element therein and has a sealingsurface which forms a sealing section together with said installationsection at the front in a direction in which said sensor element ininserted, and a rotating member which has a thread section which isformed outside said rotating member and is screwed into saidinstallation section and can be rotated concentrically with respect to acentral axis of said housing; and installing said gas sensor in saidinstallation section by screwing said rotating member; wherein a releasetorque of said rotating member at 850° C. (1123 K) is 9 N·m or more; andwherein an estimated value X₁₁ of a gap formed between said sealingsurface of said housing and a sealing surface of said installationsection at 850° C. (1123 K), that is calculated according to thefollowing equation, is 31 μm or less:  X ₁₁(μm)={(L ₁×α₁)−(L ₄×α₄)−(L₅×α₅)}×1123; wherein X₁₁ represents an estimated value (μm) of said gap,L₁ represents a length (μm) from said sealing surface of saidinstallation section to a top end of said installation section, L₄represents a length (μm) from a bottom end to a top end of said threadsection, L₅ represents a length (μm) from said sealing surface of saidhousing to the bottom end of said thread section, α₁ represents acoefficient of thermal expansion (×10⁻⁶/° C.) of said installationsection, α₄ represents a coefficient of thermal expansion (×10⁻⁶/° C.)of said rotating member, and α₅ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of said housing.
 10. The method for installing agas sensor according to claim 9, wherein said sealing section is formedthrough a gasket and said rotating member is screwed in saidinstallation step so that an estimated value X₁₂ of the gap, that iscalculated according to the following equation, is 31 μm or less:X ₁₂(μm)={(L ₁×α₁)−(L ₃×α₃)−(L ₄×α₄)−(L₅×α₅)}×1123; wherein X₁₂represents an estimated value (μm) of said gap, L₁ represents a length(μm) from said sealing surface of said installation section to a top endof said installation section, L₃ represents a thickness (μm) of saidgasket, L₄ represents a length (μm) from a bottom end to a top end ofsaid thread section, L₅ represents a length (μm) from said sealingsurface of said housing to the bottom end of said thread section, α₁represents a coefficient of thermal expansion (×10⁻⁶/° C.) of saidinstallation section, α₃ represents a coefficient of thermal expansion(×10⁻⁶/° C.) of the gasket, α₄ represents a coefficient of thermalexpansion (×10⁻⁶/° C.) of said rotating member, and α₅ represents acoefficient of thermal expansion (×10⁻⁶/° C.) of said housing.